Method and apparatus for controlling the air-fuel ratio in an internal-combustion engine

Abstract

In an internal-combustion engine disposed in a vehicle, when the engine is in an idle state and the vehicle speed is not equal to zero and is less than a predetermined value, the air-fuel ratio of the engine is controlled so that the air-fuel mixture is on the lean side of the stoichiometric air-fuel ratio. In addition, even after the vehicle speed becomes zero, the air-fuel ratio is controlled so that the air-fuel mixture is on the lean side for a predetermined time period.

We claim: 
     
       1. A method for controlling the air-fuel ratio in an internal-combustion engine disposed in a vehicle, comprising the steps of: detecting whether or not said engine is in an idle state;   detecting whether or not the speed of said vehicle is greater than a predetermined value;   detecting whether or not the speed of said vehicle is zero;   measuring an elapsed timer period, depending upon the speed of said vehicle being zero;   detecting a specific component concentration in the exhaust gas of said engine to generate an air-fuel ratio signal depending upon whether the air-fuel mixture of said engine is on the rich side or on the lean side;   controlling the feedback of the air-fuel ratio of said engine so that said air-fuel ratio is close to the stoichiometric air-fuel ratio by using said air-fuel ratio signal, depending upon said engine being in the idle state or upon the speed of said vehicle being equal to or greater than said predetermined value; and   controlling the air-fuel ratio of said engine so that said air-fuel mixture is on the lean side, depending upon said engine being in the idle state and the speed of said vehicle being not zero and less than said predetermined value, or depending upon said engine being in the idle state and said elapsed time period being less than a predetermined time period.   
     
     
       2. A method as set forth in claim 1, wherein the step of controlling said air-fuel ratio so that the air-fuel mixture is on the lean side includes the steps of: decreasing the air-fuel ratio correction factor depending upon whether or not said air-fuel ratio signal indicates that the air-fuel mixture is on the rich side;   increasing the air-fuel ratio correction factor depending upon whether or not said air-fuel ratio signal indicates that the air-fuel mixture is on the lean side;   decreasing rapidly the air-fuel ratio correction factor depending upon whether or not said air-fuel ratio signal indicates that the air-fuel mixture has changed from the lean side to the rich side; and   calculating a fuel-injection amount depending on the air-fuel ratio correction factor.   
     
     
       3. A method as set forth in claim 1, wherein said step of controlling the air-fuel ratio so that the air-fuel mixture is on the lean side includes the steps of: increasing the air-fuel ratio correction factor regardless of whether said air-fuel ratio signal indicates that the air-fuel mixture is on the lean side or on the rich side;   decreasing rapidly the air-fuel ratio correction factor depending upon whether or not said air-fuel mixture changes from the lean side to the rich side; and   calculating a fuel-injection amount depending on the air-fuel ratio correction factor.   
     
     
       4. A method as set forth in claim 3, wherein said step of controlling the air-fuel ratio so that the air-fuel mixture is on the lean side further includes the steps of: measuring an elapsed time period, depending upon whether or not said air-fuel mixture is on the rich side; and   decreasing rapidly the air-fuel ratio correction factor depending upon said elapsed time period being greater than a predetermined time period.   
     
     
       5. A method as set forth in claim 1, wherein said step of controlling the air-fuel ratio so that the air-fuel mixture is on the lean side includes the steps of: detecting the intake-air amount of said engine;   detecting the rotational speed of said engine;   calculating an air-fuel ratio correction factor depending upon the detected intake-air amount and the detected rotational speed; and   calculating a fuel-injection amount depending on the caluculated air-fuel ratio correction factor.   
     
     
       6. A method as set forth in claim 1, wherein said step of controlling the air-fuel ratio so that the air-fuel mixture is on the lean side includes the steps of: decreasing the air-fuel ratio correction factor calculated in said step of controlling the air-fuel ratio feedback by a predetermined value;   holding the decreased air-fuel ratio correction factor; and   calculating a fuel-injection amount depending on the held air-fuel ratio correction factor.   
     
     
       7. An apparatus for controlling the air-fuel ratio in an internal-combustion engine disposed in a vehicle, comprising: means for detecting whether or not said engine is in an idle state;   means for detecting whether or not the speed of said vehicle is greater than a predetermined value;   means for detecting whether or not the speed of said vehicle is zero;   means for measuring an elapsed time period, depending upon the speed of said vehicle being zero;   means for detecting a specific component concentration in the exhaust gas of said engine to generate an air-fuel ratio signal depending upon whether the air-fuel mixture of said engine is on the rich side or on the lean side;   means for controlling the feedback of the air-fuel ratio of said engine so that said air-fuel ratio is close to the stoichiometric air-fuel ratio by using said air-fuel ratio signal, depending upon said engine being in the idle state or upon the speed of said vehicle being equal to or greater than said predetermined value; and   means for controlling the air-fuel ratio of said engine so that said air-fuel mixture is on the lean side, depending upon said engine being in the idle state and the speed of said vehicle being not zero and less than said predetermined value, or depending upon said engine being in the idle state and said elapsed time period being less than a predetermined time period.   
     
     
       8. An apparatus as set forth in claim 7, wherein said means for controlling the air-fuel ratio so that the air-fuel mixture is on the lean side includes: means for decreasing the air-fuel ratio correction factor depending upon whether or not said air-fuel ratio signal indicates that the air-fuel mixture is on the rich side;   means for increasing the air-fuel ratio correction factor depending upon whether or not said air-fuel ratio signal indicates that the air-fuel mixture is on the lean side;   means for decreasing rapidly the air-fuel ratio correction factor depending upon whether or not said air-fuel ratio signal indicates that the air-fuel mixture has changed from the lean side to the rich side; and   means for calculating a fuel-injection amount depending on the air-fuel ratio correction factor.   
     
     
       9. An apparatus as set forth in claim 7, wherein said means for controlling the air-fuel ratio so that the air-fuel mixture is on the lean side includes: means for increasing the air-fuel ratio correction factor regardless of whether said air-fuel ratio signal indicates that the air-fuel mixture is on the lean side or on the rich side;   means for decreasing rapidly the air-fuel ratio correction factor depending upon whether or not said air-fuel mixture changes from the lean side to the rich side; and   means for calculating a fuel-injection amount depending on the air-fuel ratio correction factor.   
     
     
       10. An apparatus as set forth in claim 9, wherein said means for controlling the air-fuel ratio so that the air-fuel mixture is on the lean side further includes: means for measuring an elapsed time period, depending upon whether or not said air-fuel mixture is on the rich side; and   means for decreasing rapidly the air-fuel ratio correction factor depending upon said elapsed time period being greater than a predetermined time period.   
     
     
       11. An apparatus as set forth in claim 7, wherein said means for controlling the air-fuel ratio so that the air-fuel mixture is on the lean side includes: means for detecting the intake-air amount of said engine;   means for detecting the rotational speed of said engine;   means for calculating an air-fuel ratio correction factor depending upon the detected intake-air amount and the detected rotational speed; and   means for calculating a fuel-injection amount depending on the calculated air-fuel ratio correction factor.   
     
     
       12. An apparatus as set forth in claim 7, wherein said means for controlling the air-fuel ratio so that the air fuel mixture is on the lean side includes: means for decreasing the air-fuel ratio correction factor calculated by said means for controlling the air-fuel ratio feedback by a predetermined value;   means for holding the decreased air-fuel ratio correction factor; and   means for calculating a fuel-injection amount depending on the held air-fuel ratio correction factor.